FAA's been calling them crewmembers for over 3 decades!  

If the certificate holder assigned the medical person to a duty aboard the aircraft in flight, according to the following FAA intpretation, they are in fact, crewmembers!

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/1990/Rowhuff-National%20EMS%20Pilots%20Association_1990_Legal_Interpretation.pdf

Answer to Question #1 of Example #2,: The answer to your question depends on whether the medical personnel are crewmembers or passengers during that flight. Part 1.1 of the FAR defines a crewmember as "[A] person assigned to perform duty in an aircraft during flight time. Therefore, before medical personnel can be classified as crewmembers, they must be assigned a duty by the certificate holder and that duty must be in an aircraft during flight time. Whether the medical personnel are assigned duty by the certificate holder and whether that duty is in an aircraft during flight time must be determined from the specific facts. Your letter does not provide those specific facts. However, if the medical personnel are not crewmembers according to the definition of Part 1.1 of the FAR, they would be passengers, and the flight must be conducted under Part 135 of the FAR if the certificate holder is receiving any compensation or benefit from the carriage.